But police were questioning that narrative late Monday after reviewing surveillance video they have obtained. They are now saying it's possible he wandered into traffic and was the victim of a hit-and-run collision.

Investigators don't know or aren't saying how Marterrance Albury ended up in the road, or whether they have ruled out the possibility that he indeed fell from inside the SUV that ultimately ran over his body with its back tire.

"There are still many unanswered questions," said Tampa police spokeswoman Laura McElroy earlier Monday, a statement that appeared still to apply late in the evening.

Police said Marterrance's mother left the child in the care of his 17-year-old brother while she went with a neighbor for a girl's night out Sunday. At some point, the child left the family's apartment on Florida Avenue just south of Fletcher Avenue, a complex with blond brick buildings surrounded by a security gate with bars too close, it seemed, for even a 4-year-old to squeeze through.

Sometime about 9:45 p.m. Sunday, a driver of another vehicle told police, the boy fell from the back passenger door of a green Ford Expedition heading south on N Florida Avenue near 109th Avenue. Marterrance fell onto his head and the Expedition's back tire ran over him, the witness said.

But surveillance video obtained by police Monday appeared to raise questions about that account. Investigators attempted to obtain a version with better resolution to form a more clear assessment. They are still seeking the driver of the vehicle.

The Expedition continued south, leaving Marterrance injured in the road, police said. The witness stopped and called 911. Marterrance was taken to St. Joseph's Hospital, where he later died.

About 20 minutes after the incident was reported, Marterrance's 17-year-old brother walked up to officers at the scene and said he could not find his little brother, police said.

Marterrance's mother, Johntea L. Williams, 36, had left her sons late Sunday while she went out with a neighbor, Sheavella Corley. The two women had gone to Sarasota, Corley told the Tampa Bay Times, where they spent the night together talking.

Williams returned to her apartment about 4 a.m., where officers told her what happened. She became hysterical, and made statements about wanting to end her own life, McElroy said. Williams was later taken into protective custody under the state's Baker Act.

"She's terrified, hurt beyond hurt," the boy's grandmother, Rosemary Williams, told Bay News 9. "Not a word I can tell you to explain to you. This was her baby."

Police visited businesses in the area Monday morning to see if any of them have surveillance video of the incident and have obtained at least two.

The family has had brushes with authorities in the past. The Hillsborough sheriff's child protective investigations division opened two cases involving the family, according to the Florida Department of Children and Families. Neither directly involved Marterrance.

Police were called to the apartment three months ago by the boys' mother after she had tried to discipline her 17-year-old by taking his PlayStation 3 and cellphone.

According to a Tampa police report, he had pushed his mother, grabbed her hair, slammed her to the floor and punched her. He was arrested for a misdemeanor battery and taken into custody as a juvenile.

Marterrance's father was recently released from prison, police said. He is not believed to be involved in the boy's death.

Corley, who lives across the hall from the family, said Marterrance was an adventurous little boy who gave hugs freely and liked soda. She sometimes offered him fruit instead.

Another neighbor remembers seeing him in the window often and once, in the hall, he told her a story about his dog.

"You could tell he had a real sweet heart," said Rosa Morales. "He was a gentle little boy. We're very heartbroken."

Times researcher John Martin contributed to this report. Contact Elisabeth Parker at eparker@tampabay.com or (813) 226-3431. Contact Dan Sullivan at dsullivan@tampabay.com or (813) 226-3386. Follow @TimesDan.